This invention relates to a liquid barrier dam assembly for a Mold inserts of the type to which this invention pertains are used in machines for injection molding plastic workpieces, but this invention may be useful in other fields, such as die casting and rubber molding.
This invention is disclosed for use with mold inserts of the type shown in my U.S. Pat. No. 4,828,479, granted May 9, 1989, and U.S. Pat. No. 4,959,002, granted Sep. 25, 1990, the disclosures of which are hereby incorporated by reference herein. (The ""479 and the ""002 patents are hereinafter referred to as xe2x80x9csaid patentsxe2x80x9d.) Said patents disclose generally cylindrical mold inserts for injection mold machines which have a generally cylindrical liquid channel section with a liquid conduit groove extending circumferentially around the liquid channel section. A liquid barrier is located in the groove so that the groove is double-ended, one end constituting a liquid inlet end and the other end constituting a liquid outlet end. A mold machine with which an insert is used has inlet and outlet connectors aligned with the inlet and the outlet ends of the groove so that a liquid, which is usually water, can be circulated around the insert for cooling or heating portions of the insert.
The mold inserts to which said patents relate are used in matched pairs, one being mounted on an xe2x80x9cAxe2x80x9d plate of an injection molding machine and the other mounted on its confronting xe2x80x9cBxe2x80x9d plate. Proper orientation of inserts on their respective xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d plates is maintained by interfitting keys and notches. The liquid inlets and outlets for both the xe2x80x9cAxe2x80x9d and the xe2x80x9cBxe2x80x9d plates are usually located on the same side of a master frame. If one were able to look at the liquid barriers of a pair of mutually confronting inserts from the outside of a master frame, both liquid barriers would appear to be on the same side of the master frame. However, one looking at the xe2x80x9cAxe2x80x9d plate insert from its front face would observe that its liquid barrier is on one side of the insert and, upon looking at the xe2x80x9cBxe2x80x9d plate insert from its front face, would observe that its liquid barrier is on the opposite side. Thus, for example, if the liquid barrier of the xe2x80x9cAxe2x80x9d plate insert is located at the 3:00 o""clock position, as viewed from the front face of the insert, then the liquid barrier on the xe2x80x9cBxe2x80x9d plate insert would be at the 9:00 o""clock position, as viewed from its front face.
Until machined to form the shapes of the mold cavities and cores, the only difference between an insert usable with an xe2x80x9cAxe2x80x9d plate of a mold machine and one usable with a xe2x80x9cBxe2x80x9d plate for the same machine is in regard to the location of the inlet and outlet barrier. This difference creates an inventory problem for a supplier of inserts. The practice has been to inventory inserts without the barriers and to weld dams that form the barriers into the liquid grooves when the inserts are removed from inventory for use or sale. The welding operations must be carried out with care, not only to insure that each dam is installed in the proper location, but also to insure that a dam will not, during use, slide or otherwise move around in the liquid conduit groove and will not work loose while the insert cavity or core is being machined. (The machining operations are usually done, at least in part, on turning lathes which rotate the inserts at high speeds and there is a danger that a loose dam would fly away from a rotating insert and cause injury to the lathe operator.) The use of the described welding procedure is obviously inefficient and costly because it requires the availability of a skilled welder when each insert is removed from inventory in order to insure that a liquid barrier is properly formed. Of course, an option would be to inventory inserts having inlet and outlet barriers already formed. However, that would require twice the inventory to reasonably insure that there would be an adequate supply of inserts usable with xe2x80x9cAxe2x80x9d plates and also an adequate supply of inserts usable with xe2x80x9cBxe2x80x9d plates.
The user of a mold insert often drills liquid passageways extending inwardly from circumferentially-extending liquid conduit grooves to meet various cooling or heating needs. To insure an adequate flow of liquid into such inwardly directed passageways, one or more additional dams or barriers are affixed inside the peripheral liquid conduit groove. The provision of additional dams or barriers, using the present welding procedures, can be time consuming and costly.
Accordingly, there exists a need to improve the efficiency with which inserts can be inventoried and there is also a need to enable the user of an insert to quickly, accurately and securely assemble liquid dams or barriers into liquid conduit grooves of mold inserts.
An object of this invention is to provide a liquid dam or barrier assembly which can easily, quickly, accurately, and securely installed without the use of special tools or machines, such as welders, into liquid conduit grooves extending peripherally around a mold insert.
Another object of this invention is to provide improved dam or barrier assemblies for use with mold inserts. More particularly, an object of this invention is to provide a self-contained dam assembly which includes means for clamping a dam body member to the inside surfaces of a liquid conduit groove in a mold insert utilizing locking members, such as screws or pins, moveable in bores in the dam body member which open to the outermost surfaces of the dam body member, the clamping of the dam assembly to the surfaces of the liquid conduit groove being accomplished by engaging the exposed heads of the locking members by a simple tool.
In accordance with this invention, a substantial barrier to the flow of liquid in a circumferentially-extending liquid conduit groove of a mold insert is provided by forming recesses or undercuts by undercutting the sidewalls of the liquid conduit groove, inserting a plate-like liquid dam body member within the liquid conduit groove, and clamping the dam body member in the liquid conduit groove by the use of locking members that extend through bores in the dam body member into engagement with inwardly-facing surfaces of the undercuts. The relationship between the inwardly-facing undercut surfaces and the locking members is preferably such that, during assembly, there is a progressively increasing interfering engagement of the locking members with the undercut surfaces resulting in increasing clamping pressures being applied to the dam assemblies.
More particularly, the bores in the dam body member extend therethrough in opposite directions from its top surface downwardly and outwardly toward its opposite sides. When assembled into a liquid conduit groove, the top surface of the dam body member becomes its radially outermost surface with respect to the longitudinal centerline of the insert. The dam is so sized and shaped that it fits entirely within the liquid conduit groove and is effective to substantially prevent the flow of liquid therepast. One such dam can be clamped within a liquid conduit groove to separate or define the liquid inlet and outlet ends thereof. One or more additional dams can readily be clamped within the liquid conduit groove to assist in forcing the liquid into passageways extending from the liquid conduit groove.
The undercuts in the sidewalls of the liquid conduit groove preferably extend completely through 360 degrees to enable them to be easily machined using a turning lathe and to enable the user to easily add dam assemblies at any desired location around the periphery of the liquid conduit groove. Each undercut preferably has sloping outermost surfaces that face inwardly toward the base surface of the liquid conduit groove at an angle relative to the base surface which is greater than the angles of the axes of the locking members relative to said base surface when a dam assembly is installed. Accordingly, when the locking members are driven into engagement with the inwardly-facing undercut surfaces, the leading ends of the clamping members engage and tend to gouge into the undercut surfaces. In addition, the undercuts and the dam body members are preferably so formed that the locking members engage only the sloping outermost surfaces of the undercuts. The advancement of the locking members against the inwardly-facing undercut surfaces of the undercuts is restricted only by the interference between the locking members and the inwardly-facing undercut surfaces, the parts being so formed that the locking members never engage other surfaces of the liquid conduit groove or its undercuts.
In the presently preferred embodiment of this invention the bores in the dam body members are tapped and the locking members comprise short locking screws threadedly mounted within the tapped bores. The screws are provided with heads designed to interfit with a simple tool so that the screws can easily be advanced by rotation into interfering engagement with the inwardly-facing undercut surfaces. Substantial frictional forces are generated between the screws and the inwardly-facing undercut surfaces causing the screw threads to be bent or flattened and the undercut surfaces to be roughened so that the locking screws remain tightly engaged with the undercut surfaces and the dam assembly is securely and tightly clamped in place. The use of locking screws is preferred because they are strong and reliable yet inexpensive and simple to use. Moreover, the locking screws can readily be removed, by reverse rotation, from engagement with the undercut surfaces to enable one readily to reposition or remove and replace dam assemblies.
In a modification, the locking members comprise short locking pins which are driven by force through the dam member bores, which may be smooth and not tapped, into interfering engagement with the inwardly-facing undercut surfaces. These locking pins can readily be driven by a punch. Locking pins can also be strong, reliable, inexpensive and relatively easy to use. A drawback to their use is that dam assemblies using unthreaded pins or the like are not easily repositioned or removed. However, there may be applications in which such pins would be preferred.
Other objects and advantages will become apparent from the following description and the drawings.